Flood Insurance Rate Maps (FIRMs) Study Guide¶

• Video Reference

Mapping Aspects and Coastal Applications¶

Cross-Sections and Transects¶

• Transect: A profile line running from inland across the shoreline to the limit of wave action

• Velocity Zone (V Zone): Areas with wave heights greater than 3 feet; characterized by higher velocities due to wave action

• Wave Height Zones:

  | Wave Height | Zone | Description | |-------------|------|-------------| | Greater than 3 feet | V Zone | High velocity zone with strong wave action | | Less than 3 feet | A Zone (Coastal) | Moderate wave action; sometimes called Coastal A zone or LIMWA (Limit of Moderate Wave Action) |

Wave Run-up¶

• The vertical extent waves travel up the shore beyond the still water line
• Varies based on:
  • Shoreline slope and shape
  • Storm characteristics and direction
  • Astronomical tides
  • Water depth offshore
• Important for flood risk assessment and construction considerations

Roughness and Flow Velocity¶

• Manning's Roughness Coefficient: Scale used to estimate flow velocity based on surface roughness

• Critical for calculating water velocity in channels and floodways

• Roughness varies with surface types:

  | Surface Type | Roughness Impact | |-------------|------------------| | Tall Grass | Increased roughness, slows flow | | Concrete | Low roughness, faster flow | | Regular Grass | Moderate roughness |

Floodway and Profile Details¶

• Floodways are shown on maps but usually absent on FIS
• Profiles show elevations along a river or stream, including:
  • Bridge crossings (depicted as I-beams) with bottom and top elevations
  • Flood profiles are used to determine Base Flood Elevations (BFE)

Fundamentals of Flood Insurance Rate Maps (FIRMs)¶

Community and NFIP Identification¶

• FIRMs often cover multiple communities within a county
• Each community has a unique NFIP identification number
• Map identification includes:
  • Community name
  • County name
  • NFIP ID number
• Important for documentation like elevation certificates and regulatory compliance

Map Revision Letters¶

• Each community's map revision is indicated by a letter suffix (e.g., A, B, C, D)
• Letter corresponds to revision number for that community, not the entire map
• Always check the revision letter for the latest version
• The word "revision" is not explicitly written; the letter alone signifies it

Effective Date¶

• Displayed on the front page of the map
• Using the most recent effective map is mandatory under NFIP rules
• Communities not using the latest map may violate federal regulations

Legend and Map Symbols¶

• Legend: Essential for interpreting the map, though students don't need to memorize it

• Key symbols include:

  | Symbol | Meaning | |--------|---------| | Gray box with diagonal lines | Floodway area | | Shaded areas with hole | Zone X shaded (areas of minimal flood hazard) | | Area labeled "X" (unshaded) | Zone X unshaded: areas outside flood hazard | | B Zone | Areas with flooding but less severe than A or V zones | | D Zone | Areas with possible but undetermined flood hazard |

Profile Interpretation and Applications¶

• Profiles help determine flood elevations at specific points like road crossings

• Elevation lines (500-year, 100-year, 10-year flood elevations) are shown on profiles

• Bridge crossings are precisely drawn to scale with bottom and top elevations

• Profiles allow interpolation of exact flood elevations between known points

  

Coastal Barrier Resource Areas (CBRA) and Otherwise Protected Areas (OPA)¶

• Designated coastal zones protected from development to conserve resources and reduce federal flood insurance exposure

• Effective dates: 1983, 1990, 1991 (different areas)

• Buildings constructed or substantially improved after these dates are not eligible for federal flood insurance

• Marked on flood maps by diagonal crosshatching or solid diagonal lines

• Different types of hatched areas correspond to different effective designation years

Practical Implications¶

• Existing buildings built before designation dates may have flood insurance

• Substantially damaged buildings rebuilt after the effective date cannot get flood insurance

• Communities may allow construction permits, but federal flood insurance won't be available

• This affects financing, as federally-backed loans usually require flood insurance

• Owners may need private insurance or self-insurance

Special Map Features¶

Cross Sections¶

• Slices or profiles of the floodplain used to analyze river/stream flood characteristics

• Marked by hexagons on maps and labeled with letters (A, B, C) and numbers

• Direction usually follows river flow downstream, but not always

• Check the stationing distance (reference point) on the map or profile

• Do not assume cross sections always increase in distance downstream without verification

  

Map Scale and Measurement¶

• Scales vary between maps (e.g., 500 feet, 1000 feet)
• Use a piece of paper to mark distances for rough measurements
• Some maps may not be to scale
• Always verify scale on map legend before making distance estimates

Finding Base Flood Elevation (BFE) Step-by-Step¶

1. Locate the River on the Map

   • Identify the specific river
   • Don't confuse with other rivers on the map

2. Find the Correct Cross Section

   • Cross sections marked with hexagons and letters
   • Verify you're on the correct river

   

3. Check the Floodway on the Map

   • Designated by diagonal lines
   • Base Flood Elevation in the floodway is your target

4. Read the Elevation on the FIRM

   • Locate elevation numbers along the river
   • Example: Elevation near cross section A might be approximately 10 ft

5. Consult the Profile if Needed

   • Profiles show flood elevations vs. cross sections
   • Use profile lines for 10-, 50-, 100-, and 500-year floods

   

6. Use the Floodway Data Table for Regulatory Numbers

   • For BFE in the floodway, the data table is authoritative
   • The profile may not always give the regulatory floodway elevation accurately

   

Common Pitfalls & Reminders¶

• Confusing rivers with same cross section letters: Always verify the river name
• Ignoring "floodway" in questions: Read carefully; "floodway" specifies using the floodway data table
• Misreading elevation lines on profiles: Identify the correct line style for the 100-year flood
• Assuming the first cross section with a letter is correct: Trace back to the correct river

Map Changes and Regulatory Considerations¶

Letters of Map Change (LOMC)¶

• LOMA (Letter of Map Amendment): Updates boundaries using better topography; doesn't change BFEs
• LOMR (Letter of Map Revision): Revises BFEs and boundaries due to physical changes
• CLOMR (Conditional Letter of Map Revision): Pre-approval before construction
• LOMR-F (Letter of Map Revision Based on Fill): Revises maps after fill is placed

Authority and Environmental Compliance¶

• Only FEMA can officially change flood maps
• Local governments can request changes but lack authority to make them
• Changes must consider the Endangered Species Act and other environmental regulations
• Development impacting protected species may be denied despite meeting floodplain criteria

Key Vocabulary¶

• Floodway: Channel and adjacent lands that must remain free of encroachment for base flood discharge
• Base Flood Elevation (BFE): Computed elevation of floodwater during the base (100-year) flood
• FIRM: Official map showing flood hazard areas and floodway boundaries
• Profile: Graphical representation of flood elevations along a river or stream
• Culvert: Man-made structure allowing water flow under a road or obstruction

Important Reminders¶

• Always check questions carefully to determine which source to use (profile, floodway table, or map)
• Interpret elevation data from profiles by reading the scale carefully
• Understand the difference between floodplain and floodway
• Know how to locate floodway limits on the FIRM map